HUSAT Research Institute, Loughborough University, UK

Background and objectives
Few people would argue with the notion that the end-users of a computer system should be involved in its design. It is very obvious that people who have to work with a piece of software will have useful things to say about the way it should perform. Unfortunately in practice, particularly in the development of Decision Support Systems (DSS), a user centred approach is rather rare. A contributing factor to this situation is that there are few methods around, which tell developers exactly how to make design user centred. This paper will make a first attempt to address this problem by introducing a method, tested within the DESSAC project, for the incorporation of user requirements into the DSS design process. The paper will also discuss some of the more generic findings and resultant guidelines relating to the design of the user interface.

Materials and methods
While the basic processes (capturing requirements, creating a functional specification, prototyping, testing, and iterative development) are fairly standard in mainstream software development, the DSS methodology differs in that it focuses on the questions the user needs to answer during the process of arriving at a decision. Using the Arinze model [1] , user questions can be split into 3 broad types; called state, action and projection enquiries. The advantage of this approach is that the decomposition automatically provides a description of the information the system must contain (state enquiries); an indication of the required functions (action enquiries); and the interface features (projection enquiries) that the DSS needs to possess. It also provides a very neat way of testing the developing system against its requirements i.e. if the system can't easily support the question it isn't doing its job.

Results and conclusions
In addition to the design methodology the paper will focus on user interface design issues common to most agricultural/horticultural DSS. Observations from DESSAC and other DSS related projects suggest that the agricultural/horticultural user can be characterised by:
Limited access time: DSS are of greatest benefit at times (in-season) when the intended user has least time to spare.
Occasional use: the user may only access a DSS at certain points each year.
Range of computer skills: degree of computer skill will be very variable.
Range of interest in the science: varied interest in a DSS scientific underpinnings.
Lack of familiarity with mathematical models: most users will not understand the characteristics and limitations of a modelling approach.

The problems resulting from these characteristics for the design of user interfaces will be discussed and the paper will suggest some basic guidelines for interface design using snapshots from the DESSAC system as examples.

1. Arinze B, 1989. In: Doukidis GI, Land F, and Miller G, (Eds.), Knowledge-based Management Support Systems Chichester: Ellis Horwood Ltd. 166-182.